We have to learn from each other & from the past.
The way we learn enemy tactics & how to counter them (while avoiding certain mistakes) is by gathering up the things other people have learned & figuring out how to apply them to our present & our future.
We don't just look to the past to find what DOES work. There is also a whole treasure trove of information from people who tried things that DIDN'T work, especially if they have gained insight into WHY they didn't work.